14.6.2 ClamAV Requirements and Usage Considerations

ClamAV can run on a separate system of its own, on the same system as
the Messaging Server in a single system deployment, or on the same system
as the MTA in a two-tier deployment. If Local Mail Transfer Protocol (LMTP)
is used between the MTA and the message store, the filtering must be invoked
from the MTA. It cannot be invoked from the message store. When SMTP is used
between the MTA and the message store, it can be invoked from either one.

If you want to use a farm of servers running ClamAV, use a load balancer
front of them. The MTA is configured with only one address for the ClamAV
server.